Synthesis of N-Monosubstituted Sulfondiimines by Metal-free Iminations of Sulfiliminium Salts.

Sulfondiimines are marginalized entities among nitrogencontaining organosulfur compounds, despite offering promising properties for applications in various fields including medicinal and agrochemical. Herein, we present a metal-free and rapid synthetic procedure for the synthesis of N-monosubstituted sulfondiimines that overcomes current limitations in their synthetic accessibility. Particularly, S,S-dialkyl substrates, which are commonly difficult to convert by existing methods, react well with a combination of iodine, 1,8-diazabicyclo[5.4.0]undec-7-en (DBU), and iminoiodanes (PhINR) in acetonitrile (MeCN) to furnish the corresponding sulfondiimines in yields up to 85% (25 examples). Valuable "free" NH-N'Hsulfondiimines can then be accessed by N-deprotection under mild reaction conditions. Several experimental observations suggest a mechanistic pathway diverging from the common radical-based iodine/iminoiodane mechanism. Based on the experimental results in combination with data obtained by 1H-NMR spectroscopy, ESI mass spectrometry, and crystallographic analysis we propose a direct amination from PhINNs and a reaction path via a cationic iodonitrene.

Heterometallic Au(I)-Cu(I) Clusters: Luminescence Studies and 1O2 Production.

Two different organometallic gold(I) compounds containing naphthalene and phenanthrene as fluorophores and 2-pyridyldiphenylphosphane as the ancillary ligand were synthesized (compounds 1 with naphthalene and 2 with phenanthrene). They were reacted with three different copper(I) salts with different counterions (PF6-, OTf-, and BF4-; OTf = triflate) to obtain six Au(I)/Cu(I) heterometallic clusters (compounds 1a-c for naphthalene derivatives and 2a-c for phenanthrene derivatives). The heterometallic compounds present red pure room-temperature phosphorescence in both solution, the solid state, and air-equilibrated samples, as a difference with the dual emission recorded for the gold(I) precursors 1 and 2. The presence of Au(I)-Cu(I) metallophilic contacts has been identified using single-crystal X-ray diffraction structure resolution of two of the compounds, which play a direct role in the resulting red-shifted emission with respect to the gold(I) homometallic precursors. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) polymeric matrices were doped with our luminescent compounds, and the resulting changes in their emissive properties were analyzed and compared with those previously recorded in the solution and the solid state. All complexes were tested to analyze their ability to produce 1O2 and present very good values of ΦΔ up to 50%.

Chiral carbonyl hypoiodites.

Three chiral carbonyl hypoiodites, R-C(O)OI, have been prepared from N-protected (S)-valine to give the ligand-stabilised (S)-valinoyl hypoiodite complexes with 4-dimethylaminopyridine, 4-pyrrolidinopyridine, and 4-morpholinopyridine as the stabilising ligands. The identity of the complexes was established by NMR (1H, 13C, 1H-15N HMBC) and single crystal X-ray diffraction analysis.

Revisiting the bromination of 3ß-hydroxycholest-5-ene with CBr4/PPh3 and the subsequent azidolysis of the resulting bromide, disparity in stereochemical behavior.

Cholesterol reacts under Appel conditions (CBr4/PPh3) to give 3,5-cholestadiene (elimination) and 3ß-bromocholest-5-ene (substitution with retention of configuration). Thus, the bromination of cholesterol deviates from the stereochemistry of the standard Appel mechanism due to participation of the Δ5 π-electrons. In contrast, the subsequent azidolysis (NaN3/DMF) of 3ß-bromocholest-5-ene proceeds predominantly by Walden inversion (SN2) affording 3α-azidocholest-5-ene. The structures of all relevant products were revealed by X-ray single crystal structure analyses, and the NMR data are in agreement to the reported ones. In light of these findings, we herein correct the previous stereochemical assignments reported by one of us in the Beilstein J. Org. Chem. 2015, 11, 1922-1932 and the Monatsh. Chem. 2018, 149, 505-517.

A One-Pot Domino Reaction Providing Fluorinated 5,6-Dihydro-1,2-thiazine 1-Oxides from Sulfoximines and 1-Trifluoromethylstyrenes.

N-Trifluoroacetylated (N-TFA) sulfoximines react with 1-trifluoromethylstyrenes in a one-pot domino reaction to give fluorinated 5,6-dihydro-1,2-thiazine 1-oxides in good to high yields. The process involves three sequential reaction steps that can be characterized as (1) nucleophilic allylic substitution (SN2'), (2) hydrolysis, and (3) intramolecular nucleophilic vinylic substitution (SNV). The products can further be modified by defluorination. The molecular structure of the resulting product was confirmed by X-ray crystallographic analysis.

Solid-state NMR Spectroscopy of Iodine(I) Complexes.

Solid-state NMR has been applied to a series of Barluenga-type iodine(I) [L-I-L]PF6 (L=pyridine, 4-ethylpyridine, 4-dimethylaminopyridine, isoquinoline) complexes as their hexafluorophosphate salts, as well as their respective non-liquid ligands (L), their precursor silver(I) complexes, and the respective N-methylated pyridinium and quinolinium hexafluorophoshate salts. These results are compared and contrasted to the corresponding solution studies and single-crystal X-ray structures. As the first study of its kind on the solid-state NMR behavior of halogen(I) complexes, practical considerations are also discussed to encourage wider utilization of this technique in the future.

Crotofolane Diterpenoids and Other Constituents Isolated from Croton kilwae.

Six new crotofolane diterpenoids (1-6) and 13 known compounds (7-19) were isolated from the MeOH-CH2Cl2 (1:1, v/v) extracts of the leaves and stem bark of Croton kilwae. The structures of the new compounds were elucidated by extensive analysis of spectroscopic and mass spectrometric data. The structure of crotokilwaepoxide A (1) was confirmed by single-crystal X-ray diffraction, allowing for the determination of its absolute configuration. The crude extracts and the isolated compounds were investigated for antiviral activity against respiratory syncytial virus (RSV) and human rhinovirus type-2 (HRV-2) in HEp-2 and HeLa cells, respectively, for antibacterial activity against the Gram-positive Bacillus subtilis and the Gram-negative Escherichia coli, and for antimalarial activity against the Plasmodium falciparum Dd2 strain. ent-3ß,19-Dihydroxykaur-16-ene (7) and ayanin (16) displayed anti-RSV activities with IC50 values of 10.2 and 6.1 µM, respectively, while exhibiting only modest cytotoxic effects on HEp-2 cells that resulted in selectivity indices of 4.9 and 16.4. Compounds 2 and 5 exhibited modest anti-HRV-2 activity (IC50 of 44.6 µM for both compounds), while compound 16 inhibited HRV-2 with an IC50 value of 1.8 µM. Compounds 1-3 showed promising antiplasmodial activities (80-100% inhibition) at a 50 µM concentration.

Toward Near-Infrared Emission in Pt(II)-Cyclometallated Compounds: From Excimers' Formation to Aggregation-Induced Emission.

Two series of Pt(II)-cyclometallated compounds containing N^C^N tridentate and alkynyl-chromophore ligands have been synthesized and structurally characterized. The N^C^N ligands differ on the presence of R1 = H or F in the central aromatic ring, while six different chromophores have been introduced to the alkynyl moiety. Single-crystal X-ray structures for some of the compounds reveal the presence of weak intermolecular contacts responsible for the formation of some dimers or aggregates. The photophysical characterization shows the presence of two emission bands in solution assigned to the 3π-π* transition from the N^C^N ligands mixed with 3MLCT/3ILCT transitions (higher energy band) in deaerated samples. The formation of excimers has also been identified as a broad band at longer wavelengths [near-infrared (NIR) emission] that becomes the main emission band for compounds containing phenanthrene as the chromophore. NIR emission behavior has also been explored using acetonitrile/water mixtures, and the presence of aggregates that emit at ca. 650 nm has also been detected.

The "Nitrogen Effect": Complexation with Macrocycles Potentiates Fused Heterocycles to Form Halogen Bonds in Competitive Solvents.

Weak intermolecular forces are typically very difficult to observe in highly competitive polar protic solvents as they are overwhelmed by the quantity of competing solvent. This is even more challenging for three-component ternary assemblies of pure organic compounds. In this work, we overcome these complications by leveraging the binding of fused aromatic N-heterocycles in an open resorcinarene cavity to template the formation of a three-component halogen-bonded ternary assembly in a protic polar solvent system.

Synthesis of o-Sulfinylanilines from N-Alkyl Sulfoximines and Arynes.

N-Alkyl sulfoximines react with arynes generated in situ under mild conditions providing o-sulfinylanilines in good yields. The transformation is characterized by a broad substrate scope and a good functional group tolerance. The structure of a reaction product was confirmed by single-crystal X-ray diffraction.

A Copper-Catalyzed Interrupted Domino Reaction for the Synthesis of Fused Triazolyl Benzothiadiazine-1-oxides.

Copper(I)-catalyzed domino reactions of 2-azido sulfoximines with 1-iodoalkynes yield fused triazolyl-containing benzothiadiazine-1-oxides. The protocol features the synthesis of two fused heterocyclic rings in one step with good to excellent yields and a broad functional group tolerance. Detailed mechanistic investigations indicate that a copper π-complex initiates a cycloaddition and oxidative C-N coupling reaction sequence. The results suggest an interrupted domino process involving an iodinated triazole as a key intermediate.

Intra- vs Intermolecular Aurophilic Contacts in Dinuclear Gold(I) Compounds: Impact on the Population of the Triplet Excited State.

Two series of dinuclear gold(I) complexes that contain two Au-chromophore units (chromophore = dibenzofurane or dimethylfluorene) connected through a diphosphane bridge that differs in the flexibility and length (diphosphane = dppb for 1,4-bis(diphenylphosphino)butane, DPEphos for bis[(2-diphenylphosphino)phenyl]ether, xanthphos for 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, and BiPheP for 2,2'-bis(diphenylphosphino)-1,1'-biphenyl) have been synthesized and structurally characterized. Their photophysical properties have been carefully investigated, paying attention to the role of the presence, or absence, of aurophilic contacts and their nature (intra- or intermolecular character). This analysis was permitted due to the X-ray crystallographic determination of all of the structures of the compounds discussed herein. The quantum yields of the triplet population, ϕT, have been calculated by nanosecond-laser flash photolysis measurements, and we could determine the main role of the character of the aurophilic contacts in the resulting ϕT, being especially favored in the presence of intermolecular contacts. Time-dependent density functional theory (TD-DFT) calculations support the absorption and emission assignments and the shorter distance between S1 and the closest triplet excited state energy in the case of the compounds with a higher triplet-state population.

Selective gas adsorption by calixarene-based porous octahedral M32 coordination cages.

Giant octahedral M32 coordination cages were prepared via self-assembly of sulfonylcalix[4]arene-supported tetranuclear M(II) clusters (M = Co, Ni) with hybrid linker based on tris(dipyrrinato)cobalt(III) complexes appended with peripherical carboxylic groups. Due to intrinsic and extrinsic porosity, the obtained solid-state supramolecular architectures demonstrated good performance as adsorbents for the separation of industrially important gases mixtures.

Development of gold(I) phosphorescent tweezers for sensing applications.

The synthesis of the gold(I) alkynyl-fluorene compound 2 containing a diphosphane (dppb = 1,4-bisdiphenylphosphanebutane) has been easily achieved by the treatment of the previously synthesized [2-ethynylfluorene-Au]n polymer (1) and the corresponding dppb diphosphane in an adequate 2 : 1 stoichiometry. Compound 2 shows a boat-tweezer conformation that makes it ideal for being used as a host in molecular recognition processes. Different polyaromatic hydrocarbons (PAHs) and polyfluorinated compounds (PFCs) have been used as guests and a stronger interaction has been detected for PAHs, especially for anthracene, in agreement with spectrofluorometric titrations and the calculated values of the association constants, which is confirmed by DFT calculations. Compound 2 has then been immobilized in different organic matrices, in order to enhance room temperature phosphorescence (RTP). This promotes sensing with dual emission and furthermore in the case of the analytes under investigation, phosphorescence is observed in a range of wavelengths that do not coincide with the fluorescence emission of PAHs and PFCs.

The Difficult Marriage of Triarylcorroles with Zinc and Nickel Ions.

The coordination chemistry of corrole has witnessed a great improvement in the past few years and its Periodic Table has been widened to be so large that it is compared with that of porphyrins. However, Ni and Zn ions, commonly used with porphyrins for both synthetic and theoretical purposes, are sparsely reported in the case of corroles. Here, we report synthetic protocols for preparing Ni and Zn triarylcorrole complexes. In the case of Zn, the preliminary oxidation of the free base corrole in DMSO to the neutral corrole radical is a necessary step to obtain the coordination of the metal ion, because the direct reaction led to the formation of an open-chain tetrapyrrole. The Ni complex could be directly obtained by heating the free base corrole and Ni(II) salt to 100 °C in a DMSO solution containing FeCl3. The non-innocent nature of the corrole ligand for both complexes has been elucidated by EPR, and in the case of the Zn derivative the first spectroelectrochemical characterization is presented.

Carbonyl hypoiodites from pivalic and trimesic acid and their silver(I) intermediates.

The first tris(O-I-N) carbonyl hypoiodites have been synthesised based on trimesic acid and pyridine or 4-methylpyridine, with their structures definitively confirmed by single crystal X-ray diffraction (SCXRD). The more soluble carbonyl hypoiodites based on pivalic acid have also been studied via NMR, SCXRD, and computational analyses, enabling the study of the direct silver(I) precursor and intermediates of the resulting carbonyl hypoiodites generated using a range of substituted pyridines.

Modified ent-Abietane Diterpenoids from the Leaves of Suregada zanzibariensis.

The leaf extract of Suregada zanzibariensis gave two new modified ent-abietane diterpenoids, zanzibariolides A (1) and B (2), and two known triterpenoids, simiarenol (3) and ß-amyrin (4). The structures of the isolated compounds were elucidated based on NMR and MS data analysis. Single-crystal X-ray diffraction was used to establish the absolute configurations of compounds 1 and 2. The crude leaf extract inhibited the infectivity of herpes simplex virus 2 (HSV-2, IC50 11.5 µg/mL) and showed toxicity on African green monkey kidney (GMK AH1) cells at CC50 52 µg/mL. The isolated compounds 1-3 showed no anti-HSV-2 activity and exhibited insignificant toxicity against GMK AH1 cells at ≥100 µM.

Base-promoted direct amidation of esters: beyond the current scope and practical applications.

The base-promoted direct amidation of unactivated esters is among the most useful reactions for amide bond formation in contemporary organic chemistry. The intensive research in this area has led to the development of a number of new methods to achive this transformation. However, to date, the existing literature is more methodological and in many instances lacks practical directions. Therefore, the full potential of this transformation is yet to be revealed by broadening the substrate scope. In a search for new practical applications of the amidation reaction, herein we present a comprehensive study of a number of base-promoted direct amidations that encompass a wide range of amines and esters. Furthermore, we applied our findings in the synthesis of phosphoramidates and several industrially relevant products.

The Preparation of Diaryl Sulfoxinium Triflates and Their Application in Palladium-Catalyzed Cross-Coupling Reactions.

Treatment of N-methyl-S,S-diaryl sulfoximines with methyl trifluoromethanesulfonate provides bench-stable sulfoxinium salts in excellent yields. Applying them in Sonogashira-, Heck- and Suzuki-type cross-coupling reactions leads to the corresponding products by sequential C-S bond cleavage and C-C bond formation. Electronic factors induced by substituents on the S-aryl groups govern the coupling efficiency.

Stereoselective Synthesis of Spiro-Decalin Oxindole Derivatives via Sequential Organocatalytic Michael-Domino Michael/Aldol Reaction.

A highly stereoselective procedure for the synthesis of spiro-polycyclic oxindoles bearing five contiguous stereogenic centers including two tetrasubstituted carbons has been developed. Under sequential organocatalysis performed by a pyrrolidine-based organocatalyst and DBU, a highly atom-economical Michael-domino Michael/aldol reaction sequence was optimized, yielding variously functionalized spiro-decalin oxindoles with excellent stereoselectivity (>99:1 dr, up to 92% ee).